Reevaluation of the palaeoenvironmental record of the former Komořanské jezero lake: late-glacial and Holocene palaeolimnology and vegetation development in north-western Bohemia, Czech Republic.

The main goal of this article is to summarize results of palaeoecological investigations of a classical and iconic site in the Czech Republic, the former Komořanské jezero lake. This lake persisted in north-western Bohemia from at least the Weichselian Late Glacial until quite recently. Pollen and palaeoalgological analyses of coccal green algae were carried out on several sedimentary sequences sampled within the framework of palaeobotanical and archaeological salvage research from 1970s to 1990s. The results are published here jointly for the first time. They make it possible to reconstruct both the lacustrine environment and upland vegetation in the wider surroundings of the lake. The Komořanské jezero lake in the late-glacial period was cold and oligotrophic. Its nutrient status gradually changed and became mesotrophic and dystrophic locally in the early Holocene and eutrophic from the Middle Holocene onwards. Unfortunately, big differences in geomorphology and environmental conditions together with long-distance (and likely even fluvial) transport of pollen make the reconstruction of upland vegetation somewhat difficult. Immigration of climatically demanding species into the area started already in the Preboreal period (before 8200 uncal. yr BP). Maximum expansion of broadleaved forests occurred in the Atlantic period (between 6000 and 7000 uncal. yr BP). At the same time, afforestation spreading from the lowlands (200 to 400 m altitude) up to the mountain ridges (around 1000ma.s.l.) of the Krušné hory Mts attained its maximum level. Based on continually increased presence of non-arboreal pollen we hypothesize that open grassland biotopes (continental-type steppe vegetation) persisted in the wider region from the late glacial throughout the entire Holocene. First clear evidence of a human effect on vegetation in promoting expansion of secondary grasslands is dated in pollen diagrams to around 4000 uncal. yr BP (i.e. the Subboreal period).